khash: avoid using `kh_clear` directly

src/cache.c

@@ -88,7 +88,7 @@ static void clear_cache(git_cache *cache)
 		git_cached_obj_decref(evict);
 	});
 
-	kh_clear(oid, cache->map);
+	git_oidmap_clear(cache->map);
 	git_atomic_ssize_add(&git_cache__current_storage, -cache->used_memory);
 	cache->used_memory = 0;
 }

src/pack-objects.c

@@ -197,7 +197,7 @@ static void rehash(git_packbuilder *pb)
 	size_t i;
 	int ret;
 
-	kh_clear(oid, pb->object_ix);
+	git_oidmap_clear(pb->object_ix);
 	for (i = 0, po = pb->object_list; i < pb->nr_objects; i++, po++) {
 		pos = kh_put(oid, pb->object_ix, &po->id, &ret);
 		kh_value(pb->object_ix, pos) = po;